Microstructure and properties of TA2/ Co₁₃Cr₂₈Cu₃₁Ni₂₈/ Q235 pulsed TIG weld joint

Due to the significant difference in physical and chemical properties between steel and titanium, a large number of intermetallic compounds are formed in the weld, which makes it difficult to achieve reliable connections. According to the idea of solid dissolution and high entropy of weld metal, Co₁₃Cr₂₈Cu₃₁Ni₂₈ high entropy alloy was selected as an intermediate transition layer for pulse tungsten inert gas welding of TA2 titanium and Q235 steel, the microstructure and properties of Co₁₃Cr₂₈Cu₃₁Ni₂₈ high entropy alloy and the weld joint were analyzed and studied. The results show that Co₁₃Cr₂₈Cu₃₁Ni₂₈ mainly has a two-phase face-centered cubic structure (FCC),which is cu-rich intercrystalline FCC phase and intra crystalline FCC phase, and its strength and plasticity are good. The welded joint is formed well, without stomals, cracks and other defects. The weld microstructure is composed of simple solid solution structures, which are mainly FCC phases on the Q235 side, and mainly body-centered cubic structure (BCC) and FCC phases on the TA2 side, mainly composed of BCC phases. The tensile strength of the welded joint is 224 MPa, broken at the fusion zone near the high entropy alloy on the TA2 side, this is mainly due to the formation of brittle Cr₃O₈. Many dimples and cleavage planes are observed on the fracture port, which shows certain tough fracture characteristics.